The invention relates to a method for starting an internal combustion engine, especially of a motor vehicle, wherein the engine has a piston movable in a cylinder with the piston acting on a crankshaft. The piston can run through an intake phase, a compression phase, a work phase and a discharge phase. In the method, the fuel can be injected directly into a combustion chamber in a first operating mode during a compression phase or in a second operating mode during an induction phase. The combustion chamber is delimited by the cylinder and the piston. Furthermore, the invention relates to a corresponding internal combustion engine as well as a corresponding control apparatus, especially for a motor vehicle.
A method of this kind as well as an internal combustion engine of this kind and a control apparatus of this kind are all known from U.S. Pat. No. 6,050,232.
There, during starting, the first injection is undertaken into that cylinder whose piston is in the work phase. In this way, a forward movement is imparted to the crankshaft and the engine is started. Under unfavorable conditions, such as when there is an unfavorable crankshaft angle, it is, however, possible that at least a first start attempt of the engine is not successful.
It is an object of the invention to improve the known method for starting an internal combustion engine.
This object is achieved in a method or in an internal combustion engine or in a control apparatus of the kind mentioned above in accordance with the invention in that, at standstill of the crankshaft, fuel is injected into that cylinder whose piston is in the compression phase and ignited so that the crankshaft moves backwards.
Because of this backward movement of the crankshaft, it is possible to bring the engine into a defined start position. It is therefore no longer possible that a start attempt ends in failure because of an unfavorable crankshaft angle. In lieu thereof, and via the backward movement of the crankshaft, the crankshaft is brought into a defined angular position from where the engine can be started without a starter.
In a first embodiment, the injection and/or the ignition is carried out in such a manner that the piston does not move past its rearward lower dead center point but that the movement of the crankshaft reverses itself into a forward movement. Because of the rearward movement of the crankshaft, there is no movement out of the clock frequency of the engine which is present at standstill. However, the crankshaft is at a reversal point after the rearward movement and this reversal point is defined at the start of this stroke. In this way, the engine can be started in a defined manner.
For this purpose, fuel is injected into that cylinder whose piston is located at the reversal point in the work phase and ignited at or shortly after the reversal point. A first forward movement of the crankshaft is achieved in this way.
Thereafter, fuel is injected into that cylinder whose piston is located in the reversal point in the compression phase and ignited shortly ahead or at top dead center of this piston. This is that cylinder into which, at the start, the first injection has taken place which has generated the backward movement. This affords the advantage that uncombusted mixture from the first combustion is now completely combusted. The crankshaft is further accelerated in the forward direction by the renewed injection and ignition which is present.
In a second embodiment, the injection and/or the ignition is carried out in such a manner that the piston moves beyond its rearward lower dead center point but not beyond its rearward top dead center point which follows the lower dead center point; instead, there, the movement of the crankshaft reverses into a forward movement. In contrast to the first embodiment, the crankshaft moves by one stroke rearwards. Thereafter, the crankshaft again arrives in a defined reversal point from which the engine can be started in a defined manner. Furthermore, this affords the advantage that, for the next injection and ignition, a larger air mass is present in the cylinder than in the first embodiment. From this results a larger acceleration capacity.
In the second embodiment, the subsequent starting takes place in the same manner as in the first embodiment.
Furthermore, fuel is injected into that cylinder whose piston is at the reversal point in the induction phase and ignited in the subsequent compression phase. Thereafter, fuel is injected into the cylinders and ignited in the normal sequence.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which has the capability of being run on a computer apparatus, especially on a microprocessor and is suitable for carrying out the method of the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same manner as the method for which the program is suitable for carrying out. As a control element, especially an electric storage medium can be used, for example, a flash memory or a read-only-memory.